The Facebook chief operating officer is known for advocating women in the business world. Hired by Facebook in 2008, Sandberg is credited with creating its advertising business.

Sheryl Sandberg, Facebook’s second in command, also sits on the… (Gregory Bull, Associated…)

SAN FRANCISCO — Sheryl Sandberg has become the first woman to join the board of Facebook Inc.

The Menlo Park, Calif., company announced Monday that Sandberg, its chief operating officer and one of the country's best-known female executives, would be the eighth member of what until now has been an all-boys club.

"Sheryl has been my partner in running Facebook and has been central to our growth and success over the years," Mark Zuckerberg, the company's founder and chief executive, said in a written statement. "Her understanding of our mission and long-term opportunity and her experience both at Facebook and on public company boards makes her a natural fit for our board."

The world's most popular social network has been criticized for a lack of women and minorities on its board. Most of Facebook's 901 million users are women. And Sandberg, Facebook's second in command, already sits on the board of Walt Disney Co.

Just 11% of the Fortune 500 had all-male boards last year, according to Catalyst, a New York nonprofit that monitors women's progress in the business world.

The California State Teachers' Retirement System asked Facebook in February to add a woman to its board. A petition from the advocacy group Face It urged Facebook to include women and minorities.

Sandberg, formerly a top Google executive, is known for her advocacy of women in the business world. Hired by Facebook in 2008, she is credited with creating the company's advertising business.

"Sheryl Sandberg definitely deserves to be on the Facebook board," said Anupam Palit, head of research at GreenCrest Capital. "She has brought a layer of professional management to the company, and she's in the best position to answer the questions the board will have."

"That being said," he continued, "there is a bigger issue here with Facebook. The company has been criticized for not having women and minorities in leadership positions. It seems that their answer to everything is always Sheryl Sandberg."

And, Palit said, Facebook seems to react to criticism rather than getting out in front of an issue "before it hits the media."

Sandberg's appointment will not give the board any more power or influence over the company, which is controlled by Zuckerberg, said Charles Elson, director of the Weinberg Center for Corporate Governance at the University of Delaware.

Zuckerberg has a 28% ownership stake in Facebook and controls 57% of the voting stock, giving him nearly absolute power over the company.

"It's pretty much a board that's subject to his control," Elson said. "At that point, the board basically becomes irrelevant."

"If it were a normal company, there would be some criticism of this appointment. How can a manager being monitored be on the board monitoring managers? But it's irrelevant here because of the control structure," Elson said.

Aside from Sandberg and Zuckerberg, the Facebook board comprises Donald Graham, CEO of Washington Post Co.; venture capitalist Marc Andreessen; Jim Breyer, a partner of Accel Partners; Peter Thiel, a venture capitalist and the founder of hedge fund Clarium Capital; Reed Hastings, CEO of Netflix Inc.; and Erskine Bowles, president emeritus of the University of North Carolina.